There are a number of conventional processes for packaging integrated circuits. In many packages it is desirable to attach the integrated circuit die to some type of a supporting structure (e.g. a substrate, a lead frame, a stacked die, etc.). There are a variety of methods that are commonly used to attach dice to supporting structures. In many processes, an adhesive paste is applied to either the back surface of the die or the supporting structure. More recently, wafer mount tapes have been developed that include a B-stageable adhesive film layer over a base layer. The B-stageable adhesive film is designed to adhere well enough to the back surface of a wafer before it is fully cured to hold the wafer firmly in place during wafer sawing operations. After the wafer has been diced, the base layer is activated (e.g., by exposure to UV radiation) to “release” the B-stageable adhesive layer which remains secured to the back surface of the singulated dice. The B-stageable adhesive layer may then be used as the die attach adhesive. It should be appreciated that these mounting tapes provide a good wafer level mechanism for applying an adhesive to the back surface of semiconductor dice.
There are a variety of techniques for picking singulated dice from a wafer supported by a wafer mount tape. Some existing picking techniques utilize a pin or needle type structure to push a selected die up from the backside of the wafer mount tape (i.e., by pushing up on the mounting tape underneath the selected die). The pin structure pushes the selected die up relative to its neighbors so that it may be grasped by suitable pick and place equipment. Although this approach works well in many circumstances, it can be difficult to pick very thin dice (e.g., dice having a thickness of 100 microns or less) using this approach because the needle structure may break, crack or otherwise damage the fragile dice. Another pick and place approach contemplates the use of a vacuum pickup head. Although vacuum pickup works well in many circumstances, with smaller footprint dice, it can sometimes be difficult to pick a single die at a time using a vacuum pickup head.
More recently, Nitto Denko has developed a mounting tape having an adhesive that effectively foams at a designated temperature. The foaming causes the adhesive to both lose its adhesive properties and to expand. This provides a thermal releasing adhesive that can effectively lift a die with minimal mechanical stress. These thermally releasing mount tapes are well suited for facilitating pickup in very thin chips.
Although the described techniques work well in many applications, in the semiconductor industry, there are continuing efforts to increase device yield per wafer or lot and reduce the costs and time associated with semiconductor fabrication and packaging. The present invention seeks to provide more efficient approaches to applying an adhesive layer to dice at the wafer level. The described approaches are particularly useful in handling ultra-thin chips.